The invention concerns a rotary piston tube for an x-ray radiator with a vacuum housing accommodating an anode and a cathode, and displaceable in rotation, the vacuum housing being fashioned in a frustum shaped manner and expanding towards the anode, and comprising on the expanded end a 360° all-around ray exit window connected with the anode plate of the anode.
X-ray radiators that are equipped with rotary piston tubes normally comprise a vacuum housing, positioned such that it can rotate in the radiator housing, in which a cathode arranged is arranged on one side and an anode is arranged on the other side along a common rotation axis. In the known rotary piston tubes, the vacuum housing is fashioned mostly in a piston-like manner, with a cylindrical section and an abutting, frustum-shaped section expanding towards the anode. Located around the cylindrical section and outside of the vacuum housing is a device to deflect and focus the electron beam generated by the cathode on the impinging region of the anode. The stated device is fixed with regard to the rotating vacuum housing such that the electron beam is always deflected in the same direction, and thus always impinges on the impinging region of the rotating anode. The electron beam can be focused on, for example, a line-shaped focal spot with the aid of the invention.
Rotary piston tubes of this type are, for example, specified in German Patent Documents DE 196 31 899 A1, DE 197 41 750 A1 and DE 198 10 346 C1.
To provide a targeted exit of the x-rays from the radiator housing upon rotation of the vacuum housing, such rotary piston tubes require the ray exit window in the vacuum housing to unavoidably be fashioned as a 360° all-around window. Also, so that the electron deflection functions, the main part of the vacuum housing (thus the frustum-shaped section of the vacuum housing) must be comprised of a non-magnetizable material.
In the known embodiments, the vacuum housing has been produced from a non-magnetizable, vacuum-sealed steel plate (for example, from a steel grade material with the German material number W. No. 1.4301). The wall thickness of the vacuum housing in these embodiments goes down to approximately 2 mm, whereby for reasons of rigidity, the same wall thickness (or only a slightly reduced wall thickness) is provided in the region of the exit window. Due to the mechanical stressing of the tube (the tube rotates in operation with up to approximately 9000 RPM), for reasons of rigidity, and also due to the danger of a warpage upon heating of the tube, it is not possible to dimension the exit window in this material significantly thinner than 0.5 mm (in order to be able to reduce the radiation loss) given the materials used up to now.
Furthermore, previously no measures for improved (i.e., more efficient in terms of production and maintenance) fashioning of the ray exit window have been achieved, which ultimately means that the entire tube would have to be exchanged given wearing/deterioration of the window condition as a consequence of the electron bombardment.